Cordless power tool

ABSTRACT

A cordless power tool such as a power staple gun  1  includes a power supply circuit of an electric double layer capacitor  8  and a lithium-ion battery  11 . In a standby state, the lithium-ion battery charges the electric double layer capacitor, and at a switch on time, the electric double layer capacitor supplies large current to the motor  5 . By combining the lithium-ion battery with high energy density and the electric double layer capacitor capable of discharging large current, it is possible to greatly reduce the size and weight as compared with a case where a nickel-cadmium battery or a nickel-hydrogen battery is used. Besides, since the electric double layer capacitor has a very long lifetime, the running cost can also be reduced.

TECHNICAL FIELD

The present invention relates to a cordless power tool, and particularlyto a cordless power tool in which the size and weight of a power supplypart is reduced.

BACKGROUND ART

Conventionally, a cordless power tool generally uses a battery pack of anickel-cadmium battery, a nickel-hydrogen battery or the like as a drivepower supply, and when the secondary battery mounted on a cordless powertool main body is exhausted, the cordless power tool is connected to adedicated recharger, or the battery pack removed from the cordless powertool is charged and is repeatedly used (for example, seeJP-UM-A-06-000679, JP-A-10-029172).

In the conventional cordless power tool, since the weight of thesecondary battery relative to the main body is heavy, and charging takestime, it is desired to reduce the size and weight of the power supplyand to shorten the charging time. Besides, the conventional secondarybattery has a charge/discharge lifetime of approximately several hundredto one thousand cycles, which is generally shorter than the lifetime ofthe power tool main body, and is exchanged with a new one at the timewhen the performance degrades, and accordingly, the running cost becomeshigh.

DISCLOSURE OF THE INVENTION

Thus, in order to reduce the size and weight of a cordless power tool,to shorten the charging time, and to reduce the running cost, therearise technical problems to be solved, and the invention has an objectto solve the above problems.

The invention is proposed to achieve the above object, and provides acordless power tool including an electric double layer capacitor as apower supply of a motor of the cordless power tool, in which a chargingelectrode for the electric double layer capacitor is provided in a toolmain body, and the electric double layer capacitor can be charged by anexternal recharger.

Moreover, there is provided a cordless power tool including a pluralityof electric double layer capacitors as a power supply of a motor of thecordless power tool, in which a charging electrode for the electricdouble layer capacitors is provided in a tool main body, and theelectric double layer capacitors can be charged by an externalrecharger, and further, a series parallel switching circuit to switchconnection of the plurality of electric double layer capacitors betweenseries and parallel according to a state of a start switch is provided,and when the start switch is off, the series parallel switching circuitswitches the plurality of electric double layer capacitors into theparallel connection, and when the start switch is on, the seriesparallel switching circuit switches the plurality of electric doublelayer capacitors into the series connection to supply current to themotor.

Moreover, there is provided a cordless power tool in which a secondarybattery is disposed in parallel to the electric double layer capacitors,and when the start switch is off, the secondary battery charges theelectric double layer capacitors, and when the start switch is on, theelectric double layer capacitors supply the current to the motor.

Moreover, there is provided a cordless power tool in which the secondarybattery is a small secondary battery such as a lithium ion battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of the invention and is a side view of acordless power tool.

FIG. 2 shows another embodiment and is a side view of a cordless powertool.

FIG. 3 is an electric circuit view of the cordless power tool of FIG. 2.

Incidentally, in the drawings, reference numeral 1 denotes a powerstaple gun; 2, a staple magazine part; 3, a driver mechanism part; 4, agrip part; 5, a DC motor; 6, a driver; 7, a contact arm; 8, an electricdouble layer capacitor; 9, a charging electrode; 10, a trigger lever;11, a lithium-ion battery; 12, a battery cover; and 13, a main switch.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the invention will be described in detailwith reference to the drawings. FIG. 1 shows a power staple gun 1 as anexample of a cordless power tool, in which a lower part of a housing isa staple magazine part 2, a driver mechanism part 3 is verticallydisposed at the front part (right in the drawing), and a grip part 4extends rearward from the upper back of the driver mechanism part 3. ADC motor 5 is disposed on the staple magazine part 2, and drives thedriver mechanism part 3 through a reduction gear mechanism and a cammechanism (not shown).

The driver mechanism part 3 includes a driver 6 for driving a staple anda contact arm 7 as a safety mechanism, and the contact arm 7 protrudesdownward from the lower end of the driver mechanism part 3.Incidentally, in the drawing, although the driver 6 also protrudesdownward, in the initial state, the driver 6 is pushed up to an upperstandby position by the cam mechanism in the driver mechanism 3. Thegrip part 4 includes an electric double layer capacitor 8 as a powersupply instead of a conventional general nickel-cadmium battery ornickel-hydrogen battery. The electric double layer capacitor 8 hasvolume and weight per electrical capacity, which are greatly smallerthan the secondary battery, and can reduce the size and weight of thewhole tool. Besides, it is said that the number of times of charge anddischarge thereof is several hundred thousand cycles, and the lifetimeis greatly longer than the conventional secondary battery, andaccordingly, it can be fixed in the cordless power tool, and anattachment/detachment mechanism of a battery pack becomes unnecessary.

A charging electrode 9 is exposed at the rear end surface of the powerstaple gun 1, and when the power staple gun 1 is set to a cradle of adedicated AC-DC battery recharger or a DC-DC battery recharger (notshown) with a secondary battery as a charging source, an electrode ofthe battery charger comes in contact with the charging electrode 9 ofthe power staple gun 1 and the electric double layer capacitor 8 in thepower staple gun 1 is charged. Since charging of the electric doublelayer capacitor 8 is completed in several minutes, when a user of thepower staple gun 1 carries the DC-DC battery recharger, at the time whencharging is required, the charging can be performed at that placewithout moving from the work site. Moreover, the position and shape ofthe charging electrode 8 are not particularly limited. An input jack isprovided in the power staple gun, and an output plug of a batterycharger may be connected to the input jack to perform charging.

The structure and operation of the driver mechanism part 3 areconventionally well known, and when the contact arm 7 is pressed to atarget wall surface and is pushed into the main body, a safety switch isturned on, and when a trigger lever 10 is pulled in this state, the DCmotor 5 is started. The cam mechanism in the driver mechanism part 3 isrotated to release a lock of the driver 6, and the driver 6 is pusheddown by spring force of a compression coil spring (not shown) and drivesthe first staple in the staple magazine 2 downward. After driving thestaple, the driver 6 is pulled up to the standby position by the cammechanism and is locked, the DC motor 5 is stopped, and the operation ofone cycle is completed.

In a power staple gun shown in FIG. 2, in addition to an electric doublelayer capacitor 8 as a drive power supply, a lithium-ion battery 11 ismounted as a charging power supply, and charging is performed from thelithium-ion battery 11 to the electric double layer capacitor 8. A backbattery cover 12 is opened, the lithium-ion battery 11 is mounted in abattery chamber, and when a main switch 13 is turned on, charging isperformed from the lithium-ion battery 11 to the electric double layercapacitor 8, and a standby state occurs. Thereafter, when the foregoingstart operation by a contact arm 7 and a trigger level 10 is performed,a DC motor 5 is started by electrical charge of the electric doublelayer capacitor 8 and the operation of one cycle is carried out. Afterthe end of the operation of one cycle, the DC motor 5 is stopped and theelectric double layer capacitor 8 is charged.

In the case of the above structure, when a large secondary battery ismounted, the object of reducing the size and weight can not be achieved.However, by using the lithium-ion battery 11 having energy densityhigher than a nickel-cadmium battery or a nickel-hydrogen battery, it ispossible to greatly reduce the weight as compared with a conventionalcordless power tool. Although the lithium-ion battery has a high voltage(3.6 V to 3.7 V) as compared with the nickel-cadmium battery, withrespect to large current discharge, it is inferior to the nickel-cadmiumbattery. Accordingly, although it can not be said to be suitable for theuse that a large current flows as in a power tool, when it is combinedwith the electric double layer capacitor and is used, a power supplypart which does not damage the practicability of the cordless power toolcan be constructed. However, the drive voltage of many cordless powertools is generally a high voltage of 7.2 V to 24 V, and some sort ofboosting means is required.

FIG. 3 shows a power supply circuit of the power staple gun 1 of FIG. 2,in which two electric double layer capacitors C1 and C2 are connected inparallel to a DC motor M, electric switches are provided at the plusside of the one electric double layer capacitor C1 and the minus side ofthe other electric double layer capacitor C2, respectively, and anelectric switch SW3 is provided in a bridge circuit to connect the twoelectric double layer capacitors C1 and C2 in series to each other. Thethree electric switches SW2, SW3 and SW4, and an electric switch SW1inserted between a lithium-ion battery BAT1 and the DC motor M areturned on and off by a control circuit CTRL. Incidentally, R1 denotes acurrent limiting resistor, SW11 denotes a safety switch operatingsimultaneously with the contact arm 7, and SW12 denotes a trigger switchoperating simultaneously with the trigger lever 10.

FIG. 3 shows a standby state, in which the safety switch SW11 and thetrigger switch SW12 are off, the control circuit CTRL turns on theelectric switches SW1, SW2 and SW4 and turns off the electric switchSW3, and the lithium-ion battery BAT1 charges the two parallel electricdouble layer capacitors C1 and C2. For example, in the case where thelithium-ion battery of 3.7 V is used, the two electric double layercapacitors C1 and C2 are respectively charged up to a potential of 3.7V.

Next, when the contact arm 7 is pressed to a wall surface or the likeand the safety switch SW11 is turned on, the control circuit CTRL turnsoff the electric switches SW1, SW2 and SW4, turns on the electric switchSW3, and the two electric double layer capacitors C1 and C2 areconnected in series to each other. When the trigger lever 10 is pulledand the trigger switch SW12 is turned on, current of 7.4 V is suppliedfrom the two electric double layer capacitors C1 and C2 connected inseries to each other to the DC motor M, and the power staple gun 1performs the operation of one cycle.

After the operation is ended, when the trigger lever 10 is returned andthe power staple gun 1 is separated from the wall surface or the like,the contact arm 7 goes down to the initial position, and the safetyswitch SW11 is turned off. Thereby, the control circuit CTRL turns offthe electric switch SW3 and turns on the electric switches SW1, SW2 andSW4, the two electric double layer capacitors C1 and C2 are connected inparallel to each other, the lithium-ion battery BAT1 charges the twoelectric double layer capacitors C1 and C2 and the standby state occurs.Besides, although not shown, a full charge detection circuit isprovided, and after charging is completed, the electric switch SW1 isturned off by the full charge detection circuit, and power consumptionat the standby time may be saved. Besides, when the lithium-ion batteryis discharged, as described before, the power staple gun 1 is set to acradle of a battery charger, or the lithium-ion battery 11 is removedfrom the power staple gun 1, is mounted on the battery charger and ischarged.

Incidentally, the invention is not limited to the above embodiment, andfor example, a circuit in which the lithium-ion battery BAT1 is removedfrom the charging circuit of FIG. 3 may be mounted in the power staplegun 1 of FIG. 1. Various modifications can be made within the technicalscope of the invention, and it is apparent that the invention covers themodifications.

INDUSTRIAL APPLICABILITY

As described above, since the cordless power tool of the inventionincludes the electric double layer capacitor as the power supply, thesize and weight can be remarkably reduced as compared with aconventional cordless power tool having a secondary battery as a powersupply. Further, since the charging time is short, the work efficiencyis also improved, and since the lifetime of the electric double layercapacitor is long, the running cost is also reduced.

Moreover, the plural electric double layer capacitors are included, andthe circuit is provided which switches the electric double layercapacitors so that they are connected in parallel to each other at thestandby time, and are connected in series to each other at the starttime. Accordingly, it is possible to provide the high performancecordless power tool which drives the motor by a high voltage severaltimes as high as the charging power supply.

Moreover, the secondary battery to charge the electric double layercapacitor is included, so that a continuously usable time can beextended, and for example, when a small and lightweight secondarybattery such as a lithium-ion battery is used, it is possible to reducethe size and weight as compared with a conventional cordless power toolincluding a nickel-hydrogen battery or a nickel-cadmium battery.

1. A cordless power tool comprising: a plurality of electric doublelayer capacitors mounted in a tool main body as a power supply of amotor and recharge able by an external power supply; a chargingelectrode provided in the tool main body; a contact arm; a safety switchthat is turned on when the contact arm is pressed; a trigger lever; anda trigger switch that is turned on when the trigger lever is pulled;when the safety switch and the trigger switch are off, the plurality ofelectrical double layer capacitors are connected in parallel, when thesafety switch is turned on, the plurality of electric double layercapacitors are connected in series, and when the safety switch and thetrigger switch are turned on, current is supplied from the plurality ofelectric double layer capacitors connected in series to the motor. 2.The cordless power tool according to claim 1, further comprising: asecondary battery when the safety switch and the trigger switch are off,the electric double layer capacitors are charged by the secondarybattery or the external power supply.
 3. The cordless power toolaccording to claim 2, wherein the secondary battery is a lithium-ionbattery.
 4. A cordless power tool comprising: a plurality of electricdouble layer capacitors mounted in a tool main body as a power supply ofa motor and rechargeable by an external power supply; a chargingelectrode provided in the tool main body; a series parallel switchingcircuit that switches the plurality of electric double layer capacitorsinto parallel connection when a start switch is off, and switches theplurality of electric double layer capacitors into series connectionwhen the start switch is on; a contact arm; a safety switch that isturned on when the contact arm is pressed; a trigger lever; and atrigger switch that is turned on when the trigger lever is pulled; whenthe safety switch and the trigger switch are off, the plurality ofelectric double layer capacitors are connected in parallel, when thesafety switch is turned on, the plurality of electric double layercapacitors are connected in series, and when the safety switch and thetrigger switch are turned on, current is supplied from the plurality ofelectric double layer capacitors connected in series to the motor. 5.The cordless power tool according to claim 4, further comprising: asecondary battery disposed in parallel to the electric double layercapacitors, when the start switch is off, the electric double layercapacitors are charged by the secondary battery or the external powersupply, and when the start switch is on, current is supplied from theelectric double layer capacitors to the motor.
 6. The cordless powertool according to claim 5, wherein the secondary battery is alithium-ion battery.